1. Field of the Invention
This invention relates to active filter equipment, and more particularly to improved filter equipment used as a discrete type filter, a filter for a hybrid integrated circuit, or a linear phased filter having linear phase characteristics.
2. Description of the Related Art
It is known how to selectively operate a plurality of filters having different filter characteristics as shown in FIG. 8 of the accompanying drawings. Specifically, filters 2, 4 have different characteristics (such as passbands). When an input IN1 is applied to the filter 2, a switch 6 is set to the side for the filter 2, thereby obtaining a filtered output signal OUT. On the other hand, when an input IN2 is applied to the filter 4, the switch 6 is set to the side for the filter 4, thereby obtaining a filtered output signal OUT via the filter 4.
With this arrangement, it is possible to filter a class of input signals by the filter 2 and to filter another class of input signals by the filter 4. In other words, the filters having different characteristics can be selectively operated according to the class of input signals, i.e. operation modes.
However, the more operation modes, the more filters that are needed, which means an increase in configuration, size, number of components and cost of the filters. The filters cannot operate efficiently because some filters are in operation while others are on standby.